These stock firescreens (Pfaff 4-Door, 2-Door, Gashette 2 & 4 Door, Matthews 2 & 4 Door, and Customized 2 & 4 Door) fit into your fireplace opening approximately 2½".  Therefore, you have no gaps -- your fireplace is overlapped with the flange.  This allows the firescreen to be built smaller than the opening for the piece that slides into the fireplace for the sake of allowing for expansion and fitting property if your fireplace opening is not perfectly square (they rarely are).